The National Toxicology Program has been exploring the feasibility of adopting microencapsulation for toxicology studies as a more practical and natural method of exposing laboratory animals to volatile, reactive, and/or unpalatable chemicals. In a previous dosed feed study of microencapsulated 2-ethylhexanol in Fischer 344 rats, the compound was stable in feed, and consumed at doses which are sufficient for toxicologic evaluations. Because the microencapsulation of 2-ethylhexanol did not interfere with its absorption in rats, it was concluded that this technique would be a suitable alternative for studying the oral toxicological properties of volatile chemicals in laboratory animals. A feed study of microencapsulated 2-ethylhexanol in B6C3F1 mice was performed this year. Although feed spillage by mice (probably due to the palatability of the feed mixture) prevented a determination of the actual dose received, a treatment-related increase in the activity of peroxisomal acyl CoA oxidase activity was observed.